Liquid crystal compositions

Details Liquid crystal compositions Liquid crystal compositions

1998-08-10

2001-06-12

Kelly, C. H. (Department: 1743)

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

C252S299010

Reexamination Certificate

active

06245257

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to liquid crystal compositions, and particularly to smectic liquid crystal compositions favorably used for an active element driving system. More particularly, the invention relates to “threshold value-free antiferroelectric liquid crystal compositions”.
BACKGROUND OF THE INVENTION
Attempts to use liquid crystal elements utilizing electrooptic effect of twisted nematic (TN) liquid crystals (referred to as “TN liquid crystal elements” hereinafter) as display elements of animation display devices have been heretofore made.
The TN liquid crystal elements, however, have a long (slow) electrooptic response time of several tens milliseconds. Therefore, the display devices using the TN liquid crystal elements hardly follow animation of quick motions, even when the display devices are driven by the use of active elements. Further, the angle of field of an image displayed by the use of the TN liquid crystal element is narrow, and therefore when the image displayed by the use of the TN liquid crystal element is observed with an angle beyond the fixed angle of field, a problem of an image with reversed gradation or a problem of change in color tone of the image takes place.
On the other hand, display systems not using the nematic liquid crystals but using smectic liquid crystals having higher order than the nematic liquid crystals have been proposed. For example, there are a display system using a surface stabilized ferroelectric liquid crystal, which has been reported by Clark and Lagerwall (Appl. Phys. Lett. 36, 899 (1980)), and a display system using a liquid crystal of chiral smectic CA phase known as one of antiferroelectric phases, which has been proposed by Chandani, et al. (Jpn. J. Appl. Phys., 27, L1279, 1988). These display systems can be driven with an electrooptic response time shorter by two or three figures than that of the display systems using the nematic liquid crystals, and besides, a wide angle of field can be obtained in these systems.
In the former system, however, only binary display is theoretically possible and gradation display is generally difficult. In the latter system, though the gradation display is feasible, the threshold value voltage is generally high, so that it is difficult to drive the system by the use of common active elements such as TFT.
Differently from the above-mentioned systems, a display system using a smectic liquid crystal having an applied voltage-light transmittance relationship shown by a V-shaped hysteresis curve, namely, a display system using “thresholdless antiferroelectric liquid crystal”, has been recently reported by Inui, et al. (the 21st Liquid Crystal Forum 2C04 (1995)) and Tanaka, et al. (the same forum, 2C18), and has been paid much attention. This system utilizes such a phenomenon that the directions of optic axes of the liquid crystal are uniformly changed when a voltage is applied to a liquid crystal cell wherein the liquid crystal is filled and so orientated that the smectic layer of the liquid crystal becomes perpendicular to the substrate. In this system, the voltage necessary for the response of the liquid crystal is extremely low. This system can be driven by a common active element such as TFT, and is proposed as a system capable of displaying intermediate tone (Fukuda, Asia Display '95 S6-1). Other than this liquid crystal, there is known, as a liquid crystal composition showing such properties as mentioned above, a liquid crystal composition containing a liquid crystal compound having a ferroelectric phase and an antiferroelectric phase in its phase series (referred to as an “antiferroelectric liquid crystal” hereinafter) in an amount of not less than 40% by weight and containing a liquid crystal compound having a ferroelectric phase but having no antiferroelectric phase in its phase series (referred to as a “ferroelectric liquid crystal” hereinafter), as described in Japanese Patent Laid-Open Publication No. 59624/1997. At present, however, there are very few useful thresholdless antiferroelectric liquid crystal compositions.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a novel threshold value-free antiferroelectric liquid crystal composition.
It is another object of the invention to provide a liquid crystal composition which is suitable for performing voltage gradation display by a driving system using an active element such as TFT, has an applied voltage-light transmittance relationship shown by a V-shaped hysteresis curve, and can make a quick response.
SUMMARY OF THE INVENTION
The liquid crystal composition according to the present invention is a liquid crystal composition which contains at least two compounds represented by the following formula (A) and each having different structures in an amount of not less than 50% by weight based on the total amount of all liquid crystal compounds in the liquid crystal composition, and has a transmitted light quantity I
32
satisfying the following condition (II):
0.05≦I
32
≦0.50  (II)
said transmitted light quantity I
32
being determined by the method comprising arranging two transparent substrates, each of which has a transparent electrode and at least one of which has an orientation film, in such a manner that the transparent electrodes face each other with holding a gap having a width of 2 &mgr;m therebetween, to form a cell; filling the gap with the liquid crystal composition; orientating the liquid crystal composition; placing the cell between a polarizer and an analyzer in the crossed Nicols state so that the absorption axis of the polarizer agrees with the optical axis of the liquid crystal composition under application of no voltage; measuring light transmittance at the applied voltage to obtain a hysteresis curve showing an applied voltage-light transmittance relationship of the liquid crystal composition; and applying a voltage V
32
represented by the following formula (I) to the cell filled with the liquid crystal composition to measure the transmitted light quantity I
32
;
V
32
=0.40×V
80
  (I)
wherein V
80
is an applied voltage at which the transmitted light quantity of the liquid crystal composition becomes 0.8 in the hysteresis curve in which the transmitted light quantity given when no voltage is applied is 0 and the maximum transmitted light quantity is 1;
wherein R
1
is an alkyl group of 2 to 20 carbon atoms, in which at least a part of hydrogen atoms may be substituted with halogen atoms, at least a part of methylene groups and/or halomethylene groups may be substituted with —O— groups, with the proviso that, when a part of the methylene groups and/or the halomethylene groups are substituted with —O— groups, the plural —O— groups are not adjacent to each other;
m is 0 or 1;
Z is a —COO— group or a —CH
2
O— group;
X is a hydrogen atom, a methyl group or a trifluoromethyl group; and
R
2
is a group selected from the group consisting of a straight-chain alkyl group of 1 to 5 carbon atoms, an ether group represented by —(CH
2
)
p
—O—(CH
2
)
q
CH
3
(p is an integer of 1 to 6, and q is 0 or an integer of 1 to 3) and an alkene group wherein a terminal ethyl group constituting a straight-chain alkyl group of 2 to 5 carbon atoms is replaced with a group having a C═C double bond.
In the liquid crystal composition of the invention, a compound (A-1) represented by the following formula (A-1) and a compound (A-2) represented by the following formula (A-2) are not present together; a compound (A-3) represented by the following formula (A-3) and a compound (A-7) represented by the following formula (A-7) are not present together; a compound (A-4) represented by the following formula (A-4), a compound (A-5) represented by the following formula (A-5) and a compound (A-6) represented by the following formula (A-6) are not present together; and a compound (A-7) represented by the following formula (A-7) and a compound (A-8) represented by the following formula (A-8) are not present together.
When a hysteresis curve showing an applie

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